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  • J.Kennedy ANS Global 2019 final

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Towards the decontamination of plutonium contaminated bricks: Creation of a cerium-based simulant contamination system

Research output: Contribution to conference - Without ISBN/ISSN Conference paper

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Publication date22/09/2019
Number of pages10
Pages556-565
Original languageEnglish
EventANS Global - The Westin Seattle, Seattle, United States
Duration: 22/09/201926/09/2019

Conference

ConferenceANS Global
CountryUnited States
CitySeattle
Period22/09/1926/09/19

Abstract

There is a need for the decontamination of a number of plutonium-contaminated bricks encountered in a legacy BUTEX reprocessing plant on Sellafield site in the UK. Documentary review has indicated that the source of the contamination was a 8 mol dm -3 nitric acid process stream containing 10 mmol dm -3 of Pu in either the (III) or (IV) oxidation state. Here we have sought to emulate the behaviour of Pu(III) by treatment of fired clay brick surfaces with a solution of 10 mmol dm -3 Ce(III) nitrate in 8 mol dm -3 nitric acid. XRD, porosimetry and EDX measurements of the untreated bricks reveal them to be comprised of low porosity silica and aluminosilicate phases with a surface layer of a low-Si content Al-C-N oxide derived from the atmosphere of the kiln in which the bricks were fired. Depth profiling after an initial 6 week acid soak reveals that the acid penetrates <10 mm into the brick. SEM/EDX analysis reveals that acid treatment significantly roughens the brick surface due to dissolution the above described Al-C-N oxide layer. The EDX data also shows that virtually no Ce is retained as tenacious contamination at the brick surface; this may be due to a either a mass action/kinetic effect or taken to indicate that trivalent Ce(III) is less likely to absorb at the crystalline silica/aluminosilicate surface of the brick than its more easily hydrolysable tetravalent equivalent. Preliminary higher-resolution EDX analysis indicates that small quantities of Ce(III) can be detected in pores or cracks on the surface of acid-treated brick samples. This suggests that Ce(III) may be non-tenaciously sequestered into surface defects - and that a simple salt wash may be sufficient to remove it. Based on the above observations, potential decontamination strategies are discussed and future studies outlined.